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265Chapter 16 .Window and Frame Objects The window is set up to capture all click events and invoke the doClicks() function each time the user clicks a clickable item in the window. In the doClicks() function is a single statement that instructs the first link in the document to handle the click event being passed as a parameter. The link must have an onClick event handler defined for this to be meaningful. Because an event object is passed along automatically, the link s event handler can examine event properties (for example, location of the click) and perhaps alter some of the link s properties before letting it perform its linking task. The preceding example is really showing how to use handleEvent() with a link object, rather than a window object. There is little opportunity for other objects to capture events that normally go to the window, but this method is part of every event-aware object in NN4. The corresponding method in the W3C event model s capture mechanism is dispatchEvent(), and the IE5+ equivalent is fireEvent(). Example See Chapter 29 for details and in-depth examples of working with event objects. Related Items: window.captureEvents(), window.releaseEvents(), window.routeEvent() methods; event object. home() Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . Like many of the window methods new to Navigator 4, the window.home() method provides an NN-specific scripted way of replicating the action of a toolbar button: the Home button. The action navigates the browser to whatever URL is set in the browser preferences for home page location. You cannot control the default home page of a visitor s browser. Related Items: window.back(), window.forward() methods; window.toolbar property. windowObject.home()
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264 Part III . Document Objects Reference GetAttention() Returns: Nothing. Compatibility NN2 NN3 NN4 NN6 . IE3/J1 IE3/J2 IE4 IE5 IE5.5 While the window.GetAttention() method is intended for use more by programmers of NN6 user interface themes than by scripters, the object model nevertheless exposes the method to scripters. The purpose of the method is to alert the user that the browser needs attention when the browser is not the frontmost application on the desktop. Each operating system has a different way of signalling this attention to users. Windows flashes the Taskbar rectangle for the browser window needing attention; the MacOS beeps and places a bullet next to the application s name in the Application menu. If the browser window is already the frontmost window on the desktop, then no signals flash or beep. It is highly unlikely that you would design a script that runs long enough for the user to need to switch to another application. But you might have some scripted mechanism (using the setTimeout()method described later in this chapter) that signals the user if the page has no activity for a set number of minutes. On the Example on the CD-ROM CD-ROM handleEvent(event) Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . When you explicitly capture events in the NN4 window, document, or layer object (by invoking the captureEvents() method for that object), you can control where the events go after their initial capture. To let an event continue to its original target (for example, a button that was clicked by a user), you use the routeEvent() method. But if you want to redirect an event (or class of events) to a particular event handler elsewhere in the document, use the handleEvent() method. Every NN4 object that has event handlers associated with it also has a handleEvent() method. Thus, if you are capturing click events in a window, you can redirect the events to, say, a particular button or link on the page because both of those objects know what to do with click events. Consider the following code excerpt: windowObject.handleEvent()
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263Chapter 16 .Window and Frame Objects find([ searchString [, matchCaseBoolean, searchUpBoolean]]) Returns: Boolean value for nondialog searches. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . The NN4-specific window.find() method mimics the powers of the browser s Find dialog box, accessible from the Find button in the toolbar. If you specify no parameters, the browser s Find dialog box appears, just as if the user had clicked the Find button in the toolbar. With no parameters, this function does not return a value. You can specify a search string as a parameter to the function. The search is based on simple string matching and is not in any way connected with the regular expression kind of search (see Chapter 38). If the search finds a match, the browser scrolls to that matching word and highlights the word, just as if using the browser s own Find dialog box. The function also returns a Boolean true after a match is found. If no match is found in the document or no more matches occur in the current search direction (the default direction is from top to bottom), the function returns false. Two optional Boolean parameters to the scripted find action let you specify whether the search should be case-sensitive and whether the search direction should be upward from the bottom of the document. These choices are identical to the ones that appear in the NN4 s Find dialog box. Default behavior is case- insensitive and searches from top to bottom. If you specify any one of these two optional parameters, you must specify both of them. IE4+ also has a text search facility, but it is implemented in an entirely different way (using the TextRangeobject described in Chapter 19). The visual behavior also differs in that it does not highlight and scroll to a matching string in the text. On the Example on the CD-ROM CD-ROM Related Items: TextRange, Range objects (Chapter 19). forward() See window.blur(). windowObject.forward()
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262 Part III . Document Objects Reference frame doing the capture, but then set captureEvents() and the event handler in the frame whose events you want to capture. Moreover, when a new document loads into the second frame, you must set the captureEvents()and event handler for that frame again. See Chapter 46 for details about signed scripts. On the CD-ROM Example on the CD-ROM Related Items: window.captureEvents() method; event object; signed scripts (Chapter 46). execScript( exprList [, language]) Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . The IE-specific window.execScript() method executes one or more script statements that are passed as string expressions. The first parameter is a string version of one or more script statements (multiple statements must be separated by semicolons). The second, optional parameter is the language interpreter the browser should use to execute the script statement. Acceptable values for the language are JavaScript, JScript, VBS, and VBScript. The default value is JScript, so you can omit the second parameter when supplying expressions in JavaScript. Unlike the JavaScript core language eval()function (which also executes string versions of JavaScript statements), the execScript()method returns no values. Even so, the method operates within the global variable space of the window holding the current document. For example, if a document s script declares a global variable as follows var myVar the execScript()method can read or write to that variable: window.execScript( myVar = 10; myVar += 5 ) After the above statement runs, the global variable myVar has a value of 15. On the Example on the CD-ROM CD-ROM Related Items: eval() function. windowObject.execScript()
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261Chapter 16 .Window and Frame Objects On the Example (with Figure 16-12 and Listing 16-23) on the CD-ROM CD-ROM Related Items: window.alert(), window.prompt(), form.submit() methods. createPopup() Returns: Popup Object reference. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . An IE pop-up window is a chrome-less rectangular space that overlaps the current window. Unlike the dialog boxes generated by the showModalDialog()and showModelessDialog() methods, the pop-up window s entire content must be explicitly controlled by script. That also goes for the size and location of the window. Generating the window via the createPopup()method simply creates the object in memory without displaying it. You can then use the reference to the pop-up window that is returned by the method to position the window, populate its content, and make it visible. See details in the description of the popupobject later in this chapter. On the Example on the CD-ROM CD-ROM Related Items: popup object. disableExternalCapture() enableExternalCapture() Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . NN4 security restrictions prevent one frame from monitoring events in another frame (when a different domain is in that second frame) unless the user has granted permission to a signed script. Controlling this cross-frame access requires two special window object methods: enableExternalCapture() and disableExternalCapture(). Putting these methods to work is a little trickier than manipulating the regular window.captureEvents() method. You have to turn on external capture in the windowObject.disableExternalCapture()
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260 Part III . Document Objects Reference confirm( message ) Returns: Boolean. Compatibility NN2 . NN3 . NN4 . NN6 . IE3/J1 . IE3/J2 . IE4 . IE5 . IE5.5 . A confirm dialog box presents a message in a modal dialog box along with OK and Cancel buttons. Such a dialog box can be used to ask a question of the user, usually prior to a script performing actions that will not be undoable. Querying a user about proceeding with typical Web navigation in response to user interaction on a form element is generally a disruptive waste of the user s time and attention. But for operations that may reveal a user s identity or send form data to a server, a JavaScript confirm dialog box may make a great deal of sense. Users can also accidentally click buttons, so you should provide avenues for backing out of an operation before it executes. Because this dialog box returns a Boolean value (OK = true; Cancel = false), you can use this method as a comparison expression or as an assignment expression. In a comparison expression, you nest the method within any other statement where a Boolean value is required. For example: if (confirm( Are you sure? )) { alert( OK ) } else { alert( Not OK ) } Here, the returned value of the confirm dialog box provides the desired Boolean value type for the if…else construction (Chapter 39). This method can also appear on the right side of an assignment expression, as in var adult = confirm( You certify that you are over 18 years old? ) if (adult) { //statements for adults } else { //statements for children } You cannot specify other alert icons or labels for the two buttons in JavaScript confirm dialog box windows. Tip Be careful how you word the question in the confirm dialog box. In Navigator 2 and 3, the buttons are labeled OK and Cancel in Windows browsers; the Mac versions, however, label the buttons Yes and No. If your visitors may be using older Mac Navigators, be sure your questions are logically answered with both sets of button labels. windowObject.confirm()
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259Chapter 16 .Window and Frame Objects On the Example (with Figure 16-11 and Listing 16-22) on the CD-ROM CD-ROM Related Items: window.setTimeout() method. close() Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . The window.close() method closes the browser window referenced by the window object. Most likely, you will use this method to close subwindows created from a main document window. If the call to close the window comes from a window other than the new subwindow, the original window object must maintain a record of the subwindow object. You accomplish this by storing the value returned from the window.open() method in a global variable that will be available to other objects later (for example, a variable not initialized inside a function). If, on the other hand, an object inside the new subwindow calls the window.close() method, the windowor selfreference is sufficient. Be sure to include a window as part of the reference to this method. Failure to do so may cause JavaScript to regard the statement as a document.close() method, which has different behavior (see Chapter 18). Only the window.close()method can close the window via a script. Closing a window, of course, forces the window to trigger an onUnload event handler before the window disappears from view; but after you ve initiated the window.close() method, you cannot stop it from completing its task. Moreover, onUnloadevent handlers that attempt to execute time- consuming processes (such as submitting a form in the closing window) may not complete because the window can easily close before the process completes a behavior that has no workaround (with the exception of the onBeforeUnload event handler in IE4+). While I m on the subject of closing windows, a special case exists when a subwindow tries to close the main window (via a statement such as self.opener.close()) when the main window has more than one entry in its session history. As a safety precaution against scripts closing windows they did not create, NN3+ and IE4+ ask the user whether he or she wants the main window to close (via a browser-generated dialog box). This security precaution cannot be overridden except in NN4+ via a signed script when the user grants permission to control the browser (Chapter 46). On the CD-ROM Example on the CD-ROM Related Items: window.open(), document.close() methods. windowObject.close()
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258 Part III . Document Objects Reference On the CD-ROM Example (with Listing 16-21) on the CD-ROM Related Items: window.disableExternalCapture(), window.enableExternalCapture(), window.handleEvent(), window.releaseEvents(), window.routeEvent() methods. clearInterval(intervalIDnumber) Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 Compatibility . . IE4 . IE5 . IE5.5 . Use the window.clearInterval() method to turn off an interval loop action started with the window.setInterval() method. The parameter is the ID number returned by the setInterval()method. A common application for the JavaScript interval mechanism is animation of an object on a page. If you have multiple intervals running, each has its own ID value in memory. You can turn off any interval by its ID value. As soon as an interval loop stops, your script cannot resume that interval: It must start a new one, which generates a new ID value. On the Example on the CD-ROM CD-ROM Related Items: window.setInterval(), window.setTimeout(), window.clearTimeout() methods. clearTimeout(timeoutIDnumber) Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . Use the window.clearTimeout() method in concert with the window. setTimeout() method, as described later in this chapter, when you want your script to cancel a timer that is waiting to run its expression. The parameter for this method is the ID number that the window.setTimeout() method returns when the timer starts ticking. The clearTimeout() method cancels the specified timeout. A good practice is to check your code for instances where user action may negate the need for a running timer and to stop that timer before it goes off. windowObject.clearTimeout()
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257Chapter 16 .Window and Frame Objects Note NN6 (and future browsers that implement the W3C DOM event model) has both a trickle-down and bubble-up event model combination. The syntax for using event capture in NN6 is quite different from that in NN4. The discussions of the captureEvents(), releaseEvents(), handleEvent(), and routeEvent() methods of the window, document, and layer objects apply only to Navigator 4. If your DHTML page design does not need to support NN4, you can skip these discussions. The window.captureEvents() method takes one or more event types as parameters. An event type is a constant value built inside the Navigator 4 Event object. One event type exists for every kind of event handler you see in all of the Navigator 4 document objects. The syntax is the event object name (Event) and the event name in all uppercase letters. For example, if you want the window to intercept all click events, the statement is window.captureEvents(Event.CLICK) For multiple events, add them as parameters, separated by the pipe (|) character: window.captureEvents(Event.MOUSEDOWN | Event.KEYPRESS) After an event type is captured by the windowobject, a function must be ready to deal with the event. For example, perhaps the function looks through all Event. MOUSEDOWNevents and looks to see if the right mouse button was the one that triggered the event and what form element (if any) is the intended target. The goal is to perhaps display a pop-up menu (as a separate layer) for a right-click. If the click comes from the left mouse button, the event is routed to its intended target. To associate a function with a particular event type captured by a windowobject, assign a function to the event. For example, to assign a custom doClickEvent() function to clickevents captured by the windowobject, use the following statement: window.onclick=doClickEvent Note that the function name is assigned only as a reference name (no quotes or parentheses), not like an event handler within a tag. The function itself is like any function, but it has the added benefit of automatically receiving an instance of the Event object as a parameter. To turn off event capture for one or more event types, use the window.releaseEvent() method. Note Capturing events at the window, document, or layer level in NN4 does not always work the way you might like. This is especially true if your page contains tables. For example, capturing mouse events has no effect in the Windows version of NN4 unless the cursor is atop a cell border. Event capture works most reliably when a scriptable object has an event handler defined for it (even if it is an empty string) and the element is the target of the event (for example, you are about to type into a text field). For all other elements, events may simply not be captured at the document or window level. windowObject.captureEvents()
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256 Part III . Document Objects Reference back() forward() Returns: Nothing. Compatibility NN2 NN3 NN4 . NN6 . IE3/J1 IE3/J2 IE4 IE5 IE5.5 The purpose of the window.back()and window.forward() methods in NN4 is to offer a scripted version of the global back and forward navigation buttons, while allowing the history object to control navigation strictly within a particular window or frame as it should. These window methods did not catch on in IE (and the window object is out of the scope of the W3C DOM Level 2), so you are better off staying with the historyobject s methods for navigating through browser history. For more information about version compatibility and the back and forward navigation, see the history object in Chapter 17. On the Example on the CD-ROM CD-ROM Related Items: history.back(), history.forward(), history.go() methods. captureEvents(eventTypeList) Returns: Nothing. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . In Navigator 4, an event filters down from the window object and eventually reaches its intended target. For example, if you click a button, the click event first reaches the window object; then it goes to the document object; and eventually (in a split second) it reaches the button, where an onClick event handler is ready to act on that click. The NN4 trickle-down event propagation mechanism allows window, document, and layer objects to intercept events and process them prior to reaching their intended targets (or preventing them from reaching their destinations entirely). But for one of these outer containers to grab an event, your script must instruct it to capture the type of event your application is interested in preprocessing. If you want the window object to intercept all events of a particular type, use the window.captureEvents()method to turn that facility on. windowObject.captureEvents()
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